Seeking Soy Isoflavones

Over the last decade or so, interest -- and the accompanying research into their health benefits -- in soy isoflavones has grown. They may play a key role in preventing certain cancers and also provide some of soy's protective effect to the cardiovascular and skeletal systems. Research also suggests they offer relief of menopausal symptoms, such as hot flashes, and might benefit cognitive ability. This has induced product designers to include them in functional foods, especially those targeting women's health.

Soy isoflavones belong to a class of compounds called phytoestrogens, naturally occurring plant chemicals that mimic or interact with human estrogen. Soy contains three primary isoflavones, genistein (4' 5, 7-trihydroxyisoflavone), daidzein (4', 7-dihydroxyisoflavone), and glycetein (7, 4'-dihydroxy-6-methoxyisoflavone), as well as their ß-glycosides, genistin, daidzein and glycitin. The glycosides can have an attached acetyl or malonyl group. While some argue that the aglycone form has better bioavailability than the glycosidic, the debate is more academic than nutritionally important.

Soy isoflavones exhibit a weak estrogenic effect, about 1/100 to 1/1,000 that of estradiol, a human hormone. In some cases, they also show antiestrogenic activity. Research has ascribed their benefits to hormonal as well as nonhormonal properties.

Because estrogen lowers LDL cholesterol and increases the HDL form, many researchers believe isoflavones greatly influence the cholesterol-lowering effect of soy protein. Current studies point to a combination of soy protein and isoflavones for the maximum cholesterol-lowering effect.

"In 1999, the FDA authorized a health claim linking soy protein consumption to a reduced risk of heart disease," says Greg Paul, Ph.D., director, health & nutrition, The Solae Company, St. Louis. "Since then, health claims similar to this have been approved in other countries." However, product designers need to keep in mind that the FDA allows soy protein/cardiovascular claims regardless of isoflavone content.

"While soy's heart-health benefits are well-known, a good body of research shows moderate amounts of soy may be effective in reducing the risk of various types of cancer including breast, prostate and colon, and perhaps even uterine and endometrial," says Lisa Kelly, M.P.H., R.D., communications director, United Soybean Board, Washington, D.C.

Theoretically, soy phytoestrogens might help reduce cancer risk because they lower lifetime exposure to natural estrogens by competing for receptor sites or changing the way the body breaks them down. Researchers have identified isoflavones as the reason breast-cancer rates in Japanese and Chinese women are one-fifth that of their Western counterparts. Asian women consume approximately 20 to 80 mg of isoflavones daily versus less than 5 mg per day on average for U.S. women. Currently, a health-claim petition submitted by The Solae Company linking soy protein consumption and a reduction in the risk for certain cancers is under review by the FDA.

Bone health may be another area where isoflavones can provide an advantage. Research suggests that high intakes of isoflavones may increase bone mineral density in postmenopausal women and reduce their osteoporosis risk. "According to a recent study done with SoyLife, a dose of 80 mg isoflavones --expressed as aglycones -- helped postmenopausal women maintain bone mineral concentration at the hip," says Jocelyn Mathern, R.D., technical specialist, Acatris Inc., Minneapolis. "This is consistent with other research, which has shown beneficial doses of 80 to 90 mg isoflavones for bone health. While dosage of soy isoflavones is important to consider, other factors may influence their effect on bone health. For example, researchers found that the effect of SoyLife in protecting BMC was more marked among women that were later in menopause, in women with lower body weight or among women with a lower calcium intake."

While most studies show positive results, concerns have been raised that excess soy-isoflavone consumption might promote certain problems, such as: goiters in iodine-deficient diets; reproductive problems, such as infertility; and, in some cases, promotion of existing cancer cells. However, according to Kelly: "While myths about adverse health effects of soy, such as promoting goiters or infertility have circulated for many years, in reality there is little if any scientific evidence supporting these claims. A recent review of 18 different studies concludes that soy has no effect on breast-cancer risk, except possibly when consumed during adolescence or eaten in extremely high amounts. Women at high risk for breast cancer should discuss any diet changes or concerns with their health-care provider."

Some of the confusion as to the physiological effects of isoflavones results from their varying levels in soybeans and soy ingredients. Different soybean varieties as well as agricultural factors, such as climate, can create significant isoflavone-content variation. However, processing typically makes the biggest difference. Traditional soyfoods use soy flours, concentrates and isolates produced by water extraction to best maintain isoflavone content.

"Water-extracted soy proteins are created by extracting the fat and carbohydrates from the soybean, leaving the protein portion," notes Paul. "The health benefits of soy consumption -- including its cholesterol-lowering effects -- are found in this protein matrix, which contains healthful components known as bioactives, which includes isoflavones. Because the protein matrix is preserved, therefore so are the healthful benefits of soy."

The USDA and Iowa State University have published an online database listing isoflavone content of foods (www.nal.usda.gov/fnic/   foodcomp/Data/isoflav/isoflav.html). According to the database, dry, uncooked soybeans and (water-washed) soy protein isolate average around 1.0 mg isoflavones per gram. Defatted soy flours have 1.3 mg per gram on average. The isoflavone content of alcohol-washed soy protein concentrates is significantly less that of water-washed concentrates, with an average of 0.1 mg per gram versus 1.0 mg per gram.

While regular soy products and ingredients can be a good source of isoflavones, companies looking to maximize the isoflavone content might use specialized ingredients. For example, Acatris offers soy germ isoflavone ingredients in concentrations ranging from 2% to 10%. "SoyLife offers the advantage of being made from soy germ, which is a rich source of many soy nutrients, including isoflavones," adds Mathern.

ADM, Decatur, IL, offers Novasoy, with 40% isoflavones, so adding 50 mg isoflavones per serving only requires 125 mg of the ingredient. In addition to isoflavones, it contains soy saponins, protein and other minor components. "The ratio of genistein to daidzein is 1.3:1.0 in NovaSoy, the same as in tofu," notes Patricia S. Williamson-Hughes, Ph.D., nutrition research scientist, ADM research. "These isoflavones are considered the active component in soyfoods, which are the basis for the benefit of eating a diet containing soyfoods. Therefore, it is best to have a supplement that reflects the amount of active components you would receive if you ate a diet rich in soyfoods."

The compounds are heat stable; baking or frying does not affect the total isoflavone content, although the chemical structure may change slightly -- a change that doesn't influence nutritional significance. Microbial fermentation and hydrolysis in products such as tempeh and miso means more of the isoflavones take the aglycone form.

Product designers can add soy isoflavones, whether part of soy protein or in other forms, to a wide range of products. "There are a lot of good candidates. NovaSoy is currently approved for use in healthy bars, healthy beverages and adult meal replacements," says Williamson-Hughes. The level used depends on the application. She notes that adding this ingredient at a 125 mg per serving level "is a substantial dose that would be best placed in a nutrition health bar. We recommend lower doses per serving in beverage applications."

The target amount depends on the objective. "The FDA heart health claim recommends 25 grams of soy protein per day," Paul concludes. "Associated with this intake level is approximately 50 mg of isoflavones daily. For women's health -- bone health and menopausal symptoms -- studies have shown that a daily intake of approximately 80 mg can be beneficial."

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